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6.0 OBSERVEDIll-IPACTS ON THE HYDROLOGIC SYSTEMS OF THE TRAPPER MINE <br />6.1 GROUND WATER <br />Water-quality changes in the last few years for the QR aquifer are mainly due to natural <br />variations in the recharge rate. Water-level changes in QR aquifer wells GAl, GD2, and GF6, along <br />with associated backfill wells GD3 and GF11, are close to active mining and have been influenced <br />by mining activities in addition to natural variations. The water levels in these wells declined or <br />remained steady in 1994. The decrease is in response to a drier year (7.4 inches less than 1993), <br />which resulted in decreased recharge and the reduction of dewatering activities in D pit (pit <br />pumpage and dewatering wells). These wells aze located near the downgradient toes of D and E pits <br />and/or at the interface of upgradient backfill and the downgradient native QR aquifer. These <br />positions tend to amplify water-level variations. <br />• Upgradient mining can cause water-level rises in wells downgradient of the mining by <br />allowing ground water to flow to the downgradient end of mining quicker. Also, the backfill <br />aquifers are generally more permeable than the native aquifer which also allows ground water to <br />flow faster through the backfill material resulting in more water in the aquifer at this location The <br />input of additional water to the native aquifer at the north end (toe) of the mining has decreased the <br />effects mine dewatering has had on water levels in this portion of the aquifer. <br />The water-level changes for the HI aquifer have also been influenced by variations in <br />recharge during the last few years. The mining upgradient of HI wells GBS and GF4, which <br />occurred several years ago, has been allowing the water levels in the HI aquifer to rise. Some of this <br />rise could be above pre-mine levels since these wells aze downgradient of the mining. The water- <br />levels in this azea have been fairly steady the last five years. Water levels in these two wells may <br />• have fully recovered. <br />7k-E6 <br />6-1 (Revised 09/21/95) <br />